Vacuum lock for plasma treatment of substrates

ABSTRACT

A method and apparatus for efficiently generating a gaseous plasma particularly for the treatment of substrates. A radio frequency electrical signal is applied to two electrodes disposed exteriorly of an electrically insulative, gas impervious envelope. A central passage extends into the envelope and one electrode is disposed in the central passage. The electrodes are separated at least in part by the envelope and the radio frequency signal applied to the electrodes excites the gas within the envelope to thereby generate a gaseous plasma therein. The gas conditions within the envelope differ from the gas conditions exteriorly thereof and the amplitude of the radio frequency signal is insufficient to generate a plasma outside the chamber defined by the envelope. Since the plasma does not contact the electrodes, efficiency is maximized and the plasma is not contaminated by the electrodes. In addition, the surface areas of the electrodes differ substantially thereby creating a plasma within the envelope which varies in concentration in a predetermined manner, with the concentration being greatest near the center of the envelope. A substrate may therefore be contacted by varying plasma concentration as it passes through the envelope and the outer wall of the envelope is not contaminated by the plasma. A vacuum lock for preventing gas leakage into the envelope is also disclosed.

A United States Patent [19.1

[ 1 July 16, 1974 Appl. No.: 292,455

Related US. Application Data [62] Division of Ser. No. 171,282, Aug. 12, 1971, Pat. No.

52' Us, Cl. 34/242, 34/15, 68/5 E, 68/D1G. 1, 277/237 R, 432/242 [51] Int. Cl. F26!) 25/00 [58] Field of Search 34/15, 22, 70, 151, 152,

34/155, 242; 432/115, 242; 68/5 E, DIG. l; i 277/70, 237 R [56] References Cited UNITED STATES PATENTS 3,126,724 3/1964 Kolonits 68/5 E 3,175,375 3/1965 Yazawa et al 68/5 E 3,241,343 3/1966 Yazawa 68/5 E 3,349,578 10/1967 Greer et al 68/5 E 3,460,359 8/1969 Schiffer 34/242 3,563,064 2/1971 Yazawa 68/5 E Primary Examiner-Kenneth W. Sprague Assistant Examinerlames C. Yeung [5 7 ABSTRACT A method and apparatus for efficiently generating a gaseous plasma particularly for the treatment of substrates. A radio frequency electrical signal is applied to two electrodes disposed exteriorly of an electrically insulative, gas impervious envelope. A central passage extends into the envelope and one electrode is disposed in the central passage. The electrodes are separated at least in part by the envelope and the radio frequency signal applied to the electrodes excites the gas within the envelope to thereby generate a gaseous plasma therein. The gas conditions within the envelope differ from the gas conditions exteriorly thereof and the amplitude of the radio frequency signal is insufficient to generatea plasma outside the chamber defined by the envelope. Since the plasma does not contact the electrodes, efficiency is maximized and the plasma is not contaminated by the electrodes. in addition, the surface areas of the electrodes differ substantially thereby creating a plasma within the envelope which varies in concentration in a predetermined manner, with the concentration being greatest near the center of the envelope. A substrate may therefore be contacted by varying plasma concentration as it passes through the envelope and the outer wall of the envelope is not contaminated by the plasma. A vacuum lock for preventing gas leakage into the envelope is also disclosed. I

11 Claims, 8 Drawing; Figures PATENTED JUL 2 61974 SHEET 1 0F 2 GENERATOR GENERATOR PAIENIE JUL 1 sum METEBFZ new FIG. M)

BACKGROUND OF THE INVENTION The present invention relates to a vacuum lock for apparatus for treating substrates.

It is often desirable to maintain the pressure of the gas within a reactionchamber at a pressure lower than i thatof the gas outside the chamber. The pressure differential between the interior and exterior of the chamber may create problems in introducing the substrate into the chamber. This may be a particular problem where expensive and/or harmful gases are utilized for treatment of the substrates since the escape of these gases or the leakage of undesired gases into the chamber may increase the cost of the process, result in hazardous working conditions, and/or adversely affect the treatment of the substrate.

It is therefore an object of the present invention to provide a novel method and apparatus for passing a substrate from a zone at one pressure into a-zone at another pressure without substantial leakage therebetween.

These and other objects of the present invention will become apparent to one skilled in the art to which the invention pertains from a perusal of the following description when read in conjunction with the appended drawings.

THE DRAWINGS FIG. I is a schematic representation of a reaction chamber embodying the present invention;

FIG. 2 is a view in cross section of thereaction chamber of FIG. 1, taken along the line 22;

FIG. 3 is a schematic representation of the reaction chamber of FIG. I with a substrate being treated therein;

FIG. 4 is a view in cross section of the reaction cham ber of FIG. 3, taken along the line 4-4 FIG. 5 is a schematic representation of a reaction chamber similarto the chamber shown in FIG. 3 with a plurality of substrates being treated therein;

FIG. 6 is a view in partial cross section of the reaction chamber of FIG. 5 illustrating the vacuum lock of the present invention; and,

FIGS. 7A and 7B are end views of the vacuum lock of FIG. 6, taken along the line 7-7 thereof, and illustrate two of the alternative shapes which the vacuum lock may have.

DETAILED DESCRIPTION Referring to FIGS. 1 and 2 wherein a preferred embodiment of a reaction chamber is illustrated, a reaction chamber 10 is formed by a substantially gas impervious, generally electrically non-conductive or insulative envelope 12 into which a centralpassage 14 extends. An electrode 16 extends into the central passage l4 and is isolated from the chamber 10 by the radially portion of the chamber 10, which is disposed between the electrodes 16 and 18.

A high frequency electrical potential is applied between the electrodes 16 and 18 from a suitable source such as a variable frequency and amplitude, radio frequency (RF) generator 20 to thereby subject the chamber as defined by the envelope 12 between the electrodes 16 and 18 to a selectable time varying electrical field. A suitable fill tube 22 may be provided communicating with the chamber 10 through the envelope 12 and having a valve or other suitable closure means 24 therein to selectively control the nature and pressure of the gas within the envelope 12.

With continued reference to FIGS. 1 and 2, the envelope 12 defining the chamber 10 preferably comprises an outer elongated hollow glass cylindrical member 26, an inner elongated hollow glass cylindrical member 28, and apertured end plates 30 and 32 sealed therebetween in a suitable conventional manner. The cylindrical member 28 illustrated is substantially coextensive with the member 26 and is disposed in telescoping relationship thereto coaxially within the member 26 to define a chamber annular in cross section as is shown in FIG. 2.

The central electrode 16 is preferably an elongated metallic cylindrical member, eg a wire, telescoped within the central passage 14, but may be hollow. The outer electrode 18 is preferably a hollow cylindrical electrically conductive member circumferentially disposed round at least a portion of the insulative member 26 and may, for example, be a metallic foil conformed to the radially outer surface of the envelope. The central electrode 16 preferably extends axially into the central passage 14 sufficiently so that an elongated annular portion of the chamber 10 is located between the electrodes 16 and 18.

The application of a potential between the electrodes 16 and 18 creates an electric field between these electrodes, as is indicated by the lines-34 in FIG. 2. The

' electrode configuration, i.e. the relative positions of the defining an area within the envelope l2, i.e. at least a electrodes and the relative dimensions thereof, cause the electric field to be more concentrated or dense in the vicinity of the central electrode 16 near the axis of the annular chamber 10.

If the intensity of the electric field is sufficient, the gas in the chamber 10 will be excited sufficiently to create a gaseous plasma in the chamber. The plasma generally comprises highly reactive species such as ions, electrons and neutral fragmented particles in highly excited states. Since the exciting of the gas by the electric field creates the plasma, the plasma concentration or density generally conforms to the electric field concen' tration or density. Thus, the concentration or density of the plasma generated within the gas impervious envelope 12 varies between the outer cylindrical member 26 and the inner cylindrical member 28 in a manner re lated to the electric field concentration of density.

The plasma is thereby concentrated around the inner cylindrical member 28. rather than being dispersed evenly throughout the chamber 10. This central concentration permits more efficient utilization of the plasma for treating substrates and permits selective exposure of the substrate to the plasma as will hereinafter be described. In addition, this central concentration of the plasma prevents excessive buildup of material, on the inner wall of the outer cylindrical member 26.

The relationship between the gas conditions within the envelope l2 and the gas conditions exteriorly thereof is desirably such that the plasma may be confined to the chamber 10. The electric potential applied to the electrodes 16 and 18 may thus be lower and the current density will be correspondingly less. This desirable relationship may be obtained by utilizing selected gases at predetermined pressures within the chamber 10, while exposing the electrodes outside the envelope 12 to the atmosphere.

By way of example, a monatomic inert gas, such as argon or helium at atmospheric or slightly less than atmospheric pressure may be utilized in the chamber 10. When the RF signal is applied to the electrodes 16 and 18, a plasma will be more readily generated within the chamber than exteriorly thereof. With the potential of the RF signal applied to the electrodes set at a value corresponding to the potential required to generate a plasma within the chamber 10, but below the potential required to generate a plasma in the vicinity of the electrodes l6 and 18 externally of the chamber 10, the current which flows between the electrodes 16 and 18 will not be appreciably affected by the ion flow within the highly electrically conductive plasma since these electrodes are electrically isolated from the plasma. The plasma within the chamber 10 is not contacted by the electrodes 16 and 18 and therefore not contaminated by the electrodes.

Referring now to FIG. 3, a substrate 36 to be treated within the generated plasma may be introduced into the chamber 10 through a vacuum lock 38 subsequently described in greater detail in connection with FIGS. 6 and 7. The substrate 36 may be passed through the chamber 10 in contact with the plasma therein at a rate determined by the particular treatment process to which the substrate is being subjected. For example, the substrate 36 may be an organic polymeric fiber, such as a thermoplastic or thermosetting polyester, polyamide, cellulosic or polyolefin material, the surface of which is to be treated in the plasma to obtain a particular surface modification as is described in greater detail in the previously discussed United States patent application Serial No. 93,350, by Forschirm et al. The substrate 36 may alternatively be a carbonaceous fibrous material to be treated in the plasma within the chamber 10 as is described in greater detail in the previously discussed U.S. Letters Pat. No. 3,745,104, issued July 10, 1973 to by Kenneth C. Hou. In a further application of the present invention to the treatment of substrates, a coating may be deposited on a suitable substrate by generating a suitable gaseous plasma and contacting the. substrate with this plasma. A more detailed description of the substrate and gases utilized in one such coating technique may be had by reference to the previously discussed United States Letters Pat. No. 3,677,799, issued July 18, 1972 to, by Kenneth C. Hou. The above referenced Forschirm and Hou patent applications are hereby incorporated herein by reference.

The substrate 36 maybe introduced into the chamber 10 at an at angle with respect to the central electrode 16 as is illustrated in FIG..3. The substrate 36 might thereby follow a path generally indicated at 40 which subjects the substrate 36 to varying concentrations of the plasma as it passes through the chamber 10. Alternatively, as is shown in FIG. 5, one or more substrates 36 may be passed through the chamber 10 substantially parallel to'the electrodes 16 at a selected radial distance therefrom, thereby permitting the exposure of the substrates 36 to a selected plasma concentration.

Referring now to FIGS. 6 and 7 wherein the vacuum lock 38 of FIGS. 3 and 5 is illustrated in greater detail, a hollow tube 40 sealed to the end plate 30 of the envelope 12 communicates interiorly with the chamber 10 and provides a passage through which the substrate 36 may be introduced into the chamber 10. The substrate 36 may be, for example, a loosely packed fiber bundle through which air leakage ordinarily occurs during the passage thereof between chambers at different pressures.

The tube 40 generally conforms in cross-section to the shape of the substrate, i.e. the bundle of fibers, but is slightly smaller in cross-section than the bundle causing the fibers to be inwardly compressed against each other and against the internal wall of the tube 40. For example, if the fiber bundle is generally circular in cross-section as in FIG. 7(A), the tube 40 may also be circular in cross-section with a slightly smaller diameter than that of the bundle. Likewise, if the bundle is elliptical in cross-section as in FIG. 7(B), the tube 40 preferably conforms to that .shape and is scaled down to slightly smaller dimensions.

One end 42 of the tube 40 is flared or funnel-shaped providing a transition zone for gently compressing the fiber bundle without damage thereto. If desired, the tube 40 may also narrow slightly along the length thereof to further compress the fiber bundle during the introduction thereof as illustrated in the uppermost inlet cube 38 of FIG. '5 into the chamber 10. It should be noted that when the substrate is a tightly packed fiber bundle or a single filament substrate, the diameter of the tube 40 may be the same or slightly larger than I the substrate to prevent damage thereto.

At least two fluid passages 44 and 46 are spaced along the length of the tube 40 and communicate with the interior thereof. Each of the passages 44 and 46 is connected to associated pressure sources 48 and 50,

respectively.

The gas pressure applied to the passage 46 preferably pressure applied through the passage 44 is preferably slightly higher than the pressure in the chamber 10, 7

thereby creating a pressure differential along the interior of the tube 40. This pressure differential, together with the mechanical compression of the substrate, prevents gas leakage into the chamber 10 when, for example, the pressure in the chamber 10 is less than the pressure outside the chamber 10.

With the two passages 44 and 46 illustrated in FIG. 6, gas leakage into the chamber 10 is minimized since a very slight pressure differential, e.g. 1 mm. Hg., can be maintained between the chamber 10 and the passage 46. An even smaller pressure differential between these two points may be obtained by increasing the number of lateral fluid passages 44 and 46, thereby providing even greater gas integrity between the spaces.

SUMMARY OF ADVANTAGES AND SCOPE OF THE INVENTION It is apparent from the description of the invention embodiments are therefore to be considered in all aspects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

What is claimed is:

1. Apparatus for continuously passing a substrate froma first space at a first gas pressure into a second space at a second gas pressure while maintaining the pressure differential between the spaces comprising:

* first means defining an elongated passage for providing communication between the spaces, said passage and said substrate generally conforming in cross section throughout the length of said passage; transition means at the end of said first means in the first space for introducing the substrate into said passage; and, l v

a plurality of pressure sources in fluid communication with said elongated passage at spaced points along the length thereof.

2. The apparatus of claim 1 wherein the pressure of each of said sources are different.

3. The apparatus of claim 2 wherein the second gas pressure is lower than the first gas pressure and wherein the relative pressures of said sources vary progressively from higher to lower along the length of said passage from the first space to the second space.

4. The apparatus of claim 1 wherein said first means comprises a substantially hollow, elongated tube and said transition means comprises a flared end portion on the end of said tube in the first space.

5. The apparatus of claim 4 wherein the substrate is a fiber bundle and the substrate dimensions slightly exceed the internal dimensions of said tube in crosssection whereby the substrate is mechanically com pressed as it passes through said passage.

6. The apparatus of claim 4 wherein the substrate is substantially incompressible without damage thereto and wherein the substrate dimensions are substantially equal to the internal dimensions of said tube in crosssection.

7. Sealing apparatus for passing a substrate from a first space at a first gas pressure into a second space at a-second gas pressure while maintaining the pressure differential between the spaces comprising:

a hollow tube of generally circular cross section having a substantially constant internal diameter throughout the length thereof for providing communication between the first and second spaces;

hollow transition means at the upstream end of said hollow tube for introducing the substrate into said hollow tube, said transition means having an internal diameter at the upstream end thereof larger than the internal diameter of said hollow tube and having an internal diameter at the downstream end thereof substantially equal to the internal diameter of said hollow tube; and,

pressure means influid communication with the interior of said hollow tube at spaced points along the length thereof, said means being adapted for fluid communication at one of said spaced points with a source of pressure substantially equal to the pressure of the second space.

8. The apparatus of claim 7 wherein said pressure means includes means for establishing a pressure differential between said spaced points along the length of said hollow tube.

9. Sealing apparatus for passing a substrate from a first space at a first gas pressure into a second space at a second gas pressure while maintaining the pressure differential between the spaces comprising:

a hollow tube for providing communication between the first and second spaces, the internal cross section area of said hollow tube being continuously reduced throughout the length thereof from the first space to the second space; and,

pressure means in fluid communication with the interior of said hollow tube at spaced points along the length thereof, said means being adapted for fluid communication at one of said spaced points with a source of pressure substantially equal to the pressure of the second space.

10. The apparatus of claim 9 wherein said pressure means includes means for establishing a pressure differential between said spaced points along the length of said hollow tube.

11. In a method of passing a substrate from a first space at a first gas pressure into a second space at a second gas pressure while maintaining the pressure differential between the spaces wherein the substrate is passed through an elongate hollow tube of substantially constant internal cross section, the improvement comprising the establishment of fluid communication of the interior of the hollow tube with a source of pressure at each of a plurality of spaced points along the length of the hollow tube, the pressure of the source at one of the plurality of spaced points being substantially equal to the pressure of the second space. 

1. Apparatus for continuously passing a substrate from a first space at a first gas pressure into a second space at a second gas pressure while maintaining the pressure differential between the spaces comprising: first means defining an elongated passage for providing communication between the spaces, said passage and said substrate generally conforming in cross section throughout the length of said passage; transition means at the end of said first means in the first space for introducing the substrate into said passage; and, a plurality of pressure sources in fluid communication with said elongated passage at spaced points along the length thereof.
 2. The apparatus of claim 1 wherein the pressure of each of said sources are different.
 3. The apparatus of claim 2 wherein the second gas pressure is lower than the first gas pressure and wherein the relative pressures of said sources vary progressively from higher to lower along the length of said passage from the first space to the second space.
 4. The apparatus of claim 1 wherein said first means comprises a substantially hollow, elongated tube and said transition means comprises a flared end portion on the end of said tube in the first space.
 5. The apparatus of claim 4 wherein the substrate is a fiber bundle and the substrate dimensions slightly exceed the internal dimensions of said tube in cross-section whereby the substrate is mechanically compressed as it passes through said passage.
 6. The apparatus of claim 4 wherein the substrate is substantially incompressible without damage thereto and wherein the substrate dimensions are substantially equal to the internal dimensions of said tube in cross-section.
 7. Sealing apparatus for passing a substrate from a first space at a first gas pressure into a second space at a second gas pressure while maintaining the pressure differential between the spaces comprising: a hollow tube of generally circular cross section having a substantially constant internal diameter throughout the length thereof for providing communication between the first and second spaces; hollow transition means at the upstream end of said hollow tube for introducing the substrate into said hollow tube, said transition means having an internal diameter at the upstream end thereof larger than the internal diameter of said hollow tube and having an internal diameter at the downstream end thereof substantially equal to the internal diameter of said hollow tube; and, pressure means in fluid communication with the interior of said hollow tube at spaced points along the length thereof, said means being adapted for fluid communication at one of said spaced points with a source of pressure substantially equal to the pressure of the second space.
 8. The apparatus of claim 7 wherein said pressure means includes means for establishing a pressure differential between said spaced points along the length of said hollow tube.
 9. Sealing apparatus for passing a substrate from a first space at a first gas pressure into a second space at a second gas pressure while maintaining the pressure differential between the spaces comprising: a hollow tube for providing communication between the first and second spaces, the internal cross section area of said hollow tube being continuously reduced throughout the length thereof from the first space to the second space; and, pressure means in fluid communication with the interior of said hollow tube at spaced points along the length thereof, said means being adapted for fluid communication at one of said spaced points with a source of pressure substantially equal to the pressure of the second space.
 10. The apparatus of claim 9 wherein said pressure means includes means for establishing A pressure differential between said spaced points along the length of said hollow tube.
 11. In a method of passing a substrate from a first space at a first gas pressure into a second space at a second gas pressure while maintaining the pressure differential between the spaces wherein the substrate is passed through an elongate hollow tube of substantially constant internal cross section, the improvement comprising the establishment of fluid communication of the interior of the hollow tube with a source of pressure at each of a plurality of spaced points along the length of the hollow tube, the pressure of the source at one of the plurality of spaced points being substantially equal to the pressure of the second space. 